ASTM_D_7503_-_18.pdf

Designation:D750318Standard Test Method forMeasuring the Exchange Complex and Cation ExchangeCapacity of Inorganic Fine-Grained Soils1This standard is issued under the fixed designation D7503;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope*1.1 This test method describes the procedures for measuringthe soluble and bound cations as well as the cation exchangecapacity(CEC)of fine-grained inorganic soils.Clay mineralsin fine-grained soils carry a negative surface charge that isbalanced by bound cations near the mineral surface.Thesebound cations can be exchanged by other cations in the porewater,which are referred to as soluble cations.The cationexchange capacity is a measure of the negative surface chargeon the mineral surface.The CEC generally is satisfied bycalcium(Ca),sodium(Na),magnesium(Mg),and potassium(K),although other cations may be present depending on theenvironment in which the soil exists.This test method wasdeveloped from concepts described previously in Lavkulich(1981)(1)2and Rhoades(1982)(2).In soils with appreciablegypsum or calcite,dissolution of these minerals will release Cain solution that may affect the measurement.1.2 In this test method,the soluble salts from the mineralsurface are washed off with de-ionized water and then theconcentration of soluble salts within the extract is measured.The bound cations of the clay are measured by using a solutioncontaining an index ion that forces the existing cations in thebound layer into solution.The total concentrations of boundand soluble cations in this solution are measured.The CEC ismeasured by displacing the index ion with another salt solutionand measuring the amount of the displaced index ion.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 All observed and calculated values shall conform to theguide for significant digits and rounding established in PracticeD6026.The procedures in Practice D6026 that are used tospecify how data are collected,recorded,and calculated areregarded as the industry standard.In addition,they are repre-sentative of the significant digits that should generally beretained.The procedures do not consider material variation,purpose for obtaining the data,special purpose studies,or anyconsiderations for the objectives of the user.Increasing orreducing the significant digits of reported data to be commen-surate with these considerations is common practice.Consid-eration of the significant digits to be used in analysis methodsfor engineering design is beyond the scope of this standard.1.5 UnitsThe values stated in SI units are to be regardedas standard.No other units of measurement are included in thisstandard.Reporting of test results in units other than SI shallnot be regarded as nonconformance with this test method.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:3D653 Terminology Relating to Soil,Rock,and ContainedFluidsD1193 Specification for Reagent WaterD2216 Test Methods for Laboratory Determination of Water(Moisture)Content of Soil and Rock by MassD3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD4753 Guide for Evaluating,Selecting,and Specifying Bal-ances and Standard Masses for Use in Soil,Rock,andConstruction Materials TestingD6026 Practice for Using Significant Digits in GeotechnicalDataE145 Specification for Gravity-Convection and Forced-Ventilation Ovens1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.04 on HydrologicProperties and Hydraulic Barriers.Current edition approved March 1,2018.Published March 2018.Originallyapporved in 2010.Last previous edition approved in 2010 as D750310.DOI:10.1520/D750318.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.3For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Ba